Energy yields of high explosives ranging from trinitrotoluene (TNT) to cyclotetramethylenetetranitramine (HMX) are only about 1.0 to about 1.5 (kcal/gm). Secondary burning of these high explosives in air at elevated temperatures raises the volumetric energy release to a range of about 5.6 to about 6.1 (kcal/cc). In prior attempts to improve the explosive capabilities of these materials, the addition of metals such as aluminum, uranium, or tungsten resulted in no significant improvement in energy yield or blast effectiveness. For example, in U.S. Pat. No. 3,111,439, it is disclosed that attempts have been made to increase the power of high explosives by incorporating therein finely divided aluminum, which serves to increase the amount of heat energy liberated during detonation. Upon detonation, these prior aluminized explosives release energy in the form of heat of the order of 1.2 to 1.5 times the amount of energy released during the detonation of a similar quantity of TNT. The known explosives of this type, however, are incapable of producing the maximum release of energy since sufficient quantities of aluminum are lacking, and thus portions of the available oxygen are expended on lower energy reactions.
To improve the foregoing disadvantages, and to improve the release of heat energy upon detonation by about 3 to 6.2 times the heat energy released upon the detonation of an equal weight of trinitrotoluene (TNT), one or more oxygen carriers and a metal, such as lithium or beryllium, may be added to high explosive compounds. Heat is generated upon the formation of the oxides. All of the oxygen of the carrier must be utilized in the formation of the metallic oxides to realize the improved generation of heat. However, oxygen carriers are undesirable and add to the bulk and weight of the explosive composition. Furthermore, the weight of the oxidizers dilute the explosive component by reducing the amount of explosive that can be incorporated in the explosive mass, i.e., the oxidizers occupy space that would be better occupied by explosive materials or other energy releasing components. In addition, such applications are limited by side reactions with atmospheric reactants such as water, which forms HBO2 (or HOBO) and other undesirable products that reduce heat output.
In addition to sufficient energy release, explosive compositions must also exhibit sufficient handling properties to provide safety in packaging and use and to prevent unwanted accidental detonation. Historical production of high energy materials with suitable handling properties and low risk of unwanted detonation has typically followed a few common pathways. The first is to combine a high energy material with an energetic binder such as trinitrotoluene or nitrocellulose. Such compositions reduce the amount of energetic material, but remain too unstable for modern use. A second path is to increase the amount of high energy material, but combine it with an inert binder such as an organic wax or polymer. The problem becomes finding the right balance of high energy material and inert binder to provide the necessary balance of explosive power and safety. The final approach is to synthesize new high energy compositions that may inherently possess the right balance of explosive power and insensitivity to unwanted detonation.
Further adding complexity to methods of crafting an explosive material with the proper power and safety is the fact that there are different types of packaging or uses that dictate physical characteristics of the material either during production or use. Castable explosives, as one type, are classified either as melt-cast or as plastic bonded. Melt-cast systems require the melting of the explosive, for example TNT (m.p. 81° C.), and casting into a munition. Plastic bonded systems involve a mixture of one or more explosives with a polymeric binder, casting into a munition or mold, and curing of the binder. Thus, any compositions for improving safety or handling properties of the energetic material must have the physical characteristics that allow them to function in either a melt-castable system or a plastic bonded system as desired.
The explosive formulations developed to date using the techniques described above have not yielded high energy output explosives that demonstrate a low enough susceptibility to unwanted or accidental detonation. Previous efforts have failed in this respect in that they did not discover the proper combination filler or binder (i.e. in either chemical type or concentration level) to yield these properties.
As such, there is a need for new explosive compositions with enhanced detonation yet safe handling properties.